Absorption heat-transfer system

ABSTRACT

A waste heat source ( 100 ) is used to heat a high temperature heat transfer fluid which is used to heat an absorption heat transfer machine ( 10 ) having a generator ( 20 ), an absorber ( 30 ), a condenser ( 40 ), and an evaporator ( 50 ) operatively connected together. The high temperature heat transfer fluid can also be used to heat a load ( 190 ) such as a room space or a process. The waste heat source ( 100 ) can also be used to heat an intermediate heat transfer fluid, which can be used to heat a second load ( 175 ) such as a space, a process, or an absorption heat transfer machine. Novel flow control devices ( 70, 60 ) for controlling the flow of weak solution from generator ( 20 ) to absorber ( 30 ) or of refrigerant from condenser ( 40 ) to evaporator ( 50 ), respectively, are also described.

PRIOR APPLICATION

This application claims of benefit of U.S. Provisional Application Ser.No. 60/336094, filed Nov. 30, 2001, all of which is incorporated hereinby reference as if completely written herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to absorption heat-exchange systems and moreparticularly to high-temperature waste heat recovery systems and tocontrol of weak solution and refrigerant flow in absorptionheat-exchange systems.

2. Background of the Invention

In the past, waste heat stream recovery systems have been limited to therecovery of waste heat for relatively low temperature processes, e.g.,space heating, parts cleaning, and operation of heat exchangers thatrequire an operational temperature of less than 250° F. (121° C.). Assuch, previous absorption, heat-exchange machines have been limitedtypically to a low-temperature lithium bromide-water solution pair asthe working solution.

In operating absorption heat-transfer machines, fixed restrictiondevices (orifices or capillary tubes) are used to control the flow ofweak solution (essentially devoid of refrigerant) from the high pressureside, i.e., the generator, to the low-pressure absorber. Unfortunatelysuch devices present a problem in that the flow rate may be lower thandesired during low ambients (reduced high-side pressure) or higher thandesired during high ambients (increased high side pressure). Thermalexpansion valves, which vary the refrigerant flow rate, exacerbate theproblem as the valve attempts to maintain an even low-side pressure.

Similar type problems exist with respect to refrigerant flow valveslocated between the high-pressure condenser and the low pressureevaporator. Although thermal expansion valves are available forvapor-compression systems, these valves perform poorly in absorptionsystems because of their low high-low side differential operatingpressure. A thermal expansion valve designed for 5 refrigeration tons(RT) in a vapor compression system, is capable of 7.5 RT in anabsorption system. Any attempt at using an oversized vapor-compressionsystem valve results in a poorly functioning valve with poor controlcharacteristics. Use of a smaller valve that does not match theabsorption system capacity results in higher fluid velocities that leadto premature valve failure.

As such, it is an object of the present invention to operate thegenerator of an absorption heat exchanger at a solution pair (workingfluid) temperature of greater than about 250° F. (121° C.) usingrecovered waste heat from another system.

More preferably, it is an object of the present invention to operate anabsorption heat exchange machine from waste heat at a working-fluidtemperature of greater than about 300° F. (149° C.).

Most preferably, it is an object of the present invention to operate anabsorption heat exchange machine from waste heat at a working-fluidtemperature of greater than 350° F. (177° C.).

It is a further object of the present invention to use an ammonia-wateras the working fluid (solution pair) of an absorption heat-transfermachine heated with waste heat.

It is another object of the present invention to avoid degradation ofthe performance of the waste energy heat source.

It is an object of the present invention to use a high-temperature heattransfer fluid heated with waste heat to provide simultaneous space orprocess heating and a heat source for a high temperature (above 250° F.(121° C.)) absorption heat-transfer machine that provides space orprocess cooling.

It is an object of the present invention to alternate the use of a highpressure heat transfer fluid heat source heated with waste heat betweena high-temperature absorption heat-transfer machine used for space orprocess cooling and second space or process heating.

It is an object of the present invention to provide an intermediate heattransfer loop based on waste heat recovery that also serves as a heatsource for a high-temperature absorption heat-transfer machine.

It is an object of the present invention to use an intermediate heattransfer loop based on waste heat recovery for space heating in additionto use of the waste heat as a heating source for a high-temperature,absorption heat-transfer machine.

It is an object of the present invention to use an intermediate heattransfer loop for process heating in addition to use of the waste heatas a heating source for a high-temperature, absorption heat-transfermachine.

It is an object of the present invention to use an intermediate heattransfer loop for operating a lithium bromide absorption heat-transfermachine for cooling purposes in addition to use of the waste heat as aheating source for a high-temperature absorption heat-transfer machine.

It is an object of the present invention to improve weak solution flowcontrol from the high to low pressure side of an absorption,heat-transfer machine.

It is an object of the present invention to provide a weak solution flowcontrol that ensures adequate weak solution flow from the high to lowpressure side of an absorption, heat-transfer machine without harshon/off regulation.

It is an object of the present invention to provide a weak solution flowcontrol that ensures adequate weak solution flow from the high to lowpressure side of an absorption, heat-transfer machine over a wide rangeof pressures.

SUMMARY OF THE INVENTION

These as well as other objects are meet by the present invention of anabsorption, heat-transfer system comprising a first absorptionheat-transfer machine with a generator, an absorber, a condenser, and anevaporator operatively connected together, with the generator andabsorber having a first flow control device located between them thatcontrols the flow of a weak solution from said generator to saidabsorber, with the condenser and the evaporator having a second flowcontrol device located between them that controls the flow ofrefrigerant from the condenser to the evaporator. The invention utilizesa waste-heat source that passes a waste heat stream to ahigh-temperature heat exchanger which heats a high-temperatureheat-exchange loop that comprises a pump, a heat exchange unit in thehigh-temperature heat exchanger for heating a high-temperatureheat-transfer fluid with the waste heat stream, and a second heatexchange unit located in the heat-transfer machine for heating asolution pair such as ammonia-water in the generator to a temperature ofat least about 250° F. (121° C.). Preferably, the solution pair isheated to at least 300° F. (149° C.) and most preferably to at least350° F. (177° C.).

The waste heat stream is also used to heat either another hightemperature load such as room space, a process, or another absorptionheat-transfer machine by means of the high-temperature heat-transferfluid or an intermediate temperature load which may also be a roomspace, a process, or an absorption heat-transfer machine. Theintermediate temperature load is heated with an intermediate temperatureheat transfer loop that comprises 1) an heat exchange unit for receivingheat from the waste heat stream leaving the high-temperature heatexchanger by means of an intermediate-temperature heat exchanger 2) anintermediate-temperature heat transfer fluid, 3) a pump, and 4) a secondheat exchange unit for transferring heat from theintermediate-temperature heat transfer fluid to the intermediatetemperature load.

A second heat source can be used for heating the generator of theabsorption, heat-transfer machine when the waste-heat stream isunavailable or has insufficient heat content to heat effectively thesolution pair in the generator. Lines in the high-temperature loop withappropriate fluid switching functionality such as achieved with a threeway valve permit switching of the high-temperature heat-exchange fluidbetween the generator of the absorption machine and a secondhigh-temperature load or operation of both in a concurrent fashion. Athermal storage tank can be used to store the high-temperatureheat-transfer fluid for periods when the waste-heat stream isunavailable for heating the high-temperature heat-transfer fluid. Bypasslines in the lines carrying the waste heat stream to thehigh-temperature and intermediate-temperature heat exchangers allow thewaste-heat stream to be diverted from these exchangers when thehigh-temperature or intermediate-temperature heating loops are notrequired.

A first embodiment of a flow control device for the flow of weaksolution from the generator to the absorber comprises 1) a firstrestrictor that receives weak solution from a first line connected tothe generator and passes the weak solution to the absorber by means of asecond line, 2) a second restrictor located in the first line betweenthe generator and the first restrictor, and 3) a weak solution by-passline around the second restrictor with an on-off flow device. The on-offflow device is operated by a controller which is connected to anabsorption cycle sensor such as temperature or pressure sensors mountedto determine the pressure and temperature on the high or low pressuresides of the absorption machine.

A second embodiment of the weak solution flow control devicecomprises 1) a fixed restrictor that receives weak solution from a firstline connected to the generator and passes the weak solution to theabsorber with a second line and 2) a variable restrictor positioned inthe first line between the generator and the first fixed restrictor. Thevariable restrictor comprises 1) a housing having a cylindrical boreformed in it for receiving the weak solution at a first end andoutputting the weak solution at a second end, 2) a cylindrical pistonwith a) a first end and second end that is moveably mounted in thecylindrical bore of the housing and which has a common longitudinal axiswith the housing bore, b) a bore formed in it to pass weak solution fromthe first end to said second end of the piston; and c) a valve stem atthe second end of the piston with the valve stem moveably engaging anorifice formed in said second end of the housing, typically as anorifice formed in a housing end piece; and 3) a helical springpositioned around the valve stem and contacting the second end of thepiston at one end of the spring and a shoulder of the housing at itsother end.

A refrigerant flow control device comprises 1) a thermal expansion valvethat receives refrigerant from a first line connected to the condenserand passes the refrigerant to the evaporator in a second line, and 2) afixed restrictor located in the first line between the condenser and thethermal expansion valve to reduce the inlet pressure to the thermalexpansion valve.

A second embodiment of the flow device comprises 1) a thermal expansionvalve receiving refrigerant from a first line connected to the condenserand passes the refrigerant to the evaporator in a second line; and 2) arefrigerant, by-pass line around the thermal expansion valve having afixed restrictor for passing a fix amount of refrigerant from thecondenser to the evaporator.

The foregoing and other objects, features and advantages of theinvention will become apparent from the following disclosure in whichone or more preferred embodiments of the invention are described indetail and illustrated in the accompanying drawings. It is contemplatedthat variations in procedures, structural features and arrangement ofparts may appear to a person skilled in the art without departing fromthe scope of or sacrificing any of the advantages of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the present invention illustrating theuse of a waste heat source to operate an absorption heat-transfermachine at a generator, solution-pair temperature greater than 250° F.(121° C.) to take advantage of the use of high-temperature solutionpairs such as ammonia-water in the absorption machine.

FIG. 2 is a schematic view illustrating an improved configuration forweak solution flow control from the high to the low pressure side(generator to absorber) of an absorption, heat-transfer machine such asthat shown in FIG. 1 using a by-pass loop.

FIG. 3 is a schematic view of an alternate device for improved weaksolution flow control from the high to the low pressure side (generatorto absorber) of an absorption, heat-transfer machine such as that shownin FIG. 1 using a flow control valve based system.

FIG. 4 is a cross-sectional plan view through the longitudinal axis ofthe flow control valve of FIG. 3.

FIG. 5 is a schematic view of a refrigerant flow-control device showinga fixed restriction device that allows use of a thermal expansion valvefor the flow control of refrigerant from the high to low pressure side(condenser to evaporator).

FIG. 6 is a schematic view of another embodiment of a refrigerantflow-control device showing the use of a thermal expansion valve inparallel with a fixed restriction device that provides for a minimumrefrigerant flow rate while allowing the thermal expansion valve to beused for “trim” flow control of refrigerant from the high to lowpressure side (condenser to evaporator).

In describing the preferred embodiment of the invention which isillustrated in the drawings, specific terminology is resorted to for thesake of clarity. However, it is not intended that the invention belimited to the specific terms so selected and it is to be understoodthat each specific term includes all technical equivalents that operatein a similar manner to accomplish a similar purpose.

Although a preferred embodiment of the invention has been hereindescribed, it is understood that various changes and modifications inthe illustrated and described structure can be affected withoutdeparture from the basic principles that underlie the invention. Changesand modifications of this type are therefore deemed to be circumscribedby the spirit and scope of the invention, except as the same may benecessarily modified by the appended claims or reasonable equivalentsthereof.

DETAILED DESCRIPTION OF THE INVENTION AND BEST MODE FOR CARRYING OUT THEPREFERRED EMBODIMENT

With reference to the drawings and initially FIG. 1, a waste-heatrecovery, heat-transfer device 200 comprises an absorption heat-transfermachine 10 for operation by means of a waste heat source 100 atworking-solution (solution pair) temperatures in generator 20 of greaterthan 250° F. (121° C.). In its basic form, the absorption heat-transfermachine 10 comprises an interconnected generator 20, an absorber, 30, acondenser 40, and an evaporator 50. Expansion (flow control) devices 60,70 control the flow of fluids from a high pressure to a low pressurecomponent Specifically flow control device 60 controls the flow ofrefrigerant from the high-pressure condenser 40 to the low-pressureevaporator 50. Flow control device 70 controls the flow of weak solutionfrom the high-pressure generator 20 to the low pressure absorber 30.Solution pump 24 provides strong solution from the absorber 30 to thegenerator 20.

In operation, a high-temperature solution pair (also here termed theworking fluid or strong solution) such as, but not limited towater-ammonia is heated sufficiently in generator 20 by means of a heatsource 22 to desorb a refrigerant such as ammonia from the solution pairto leave a weak solution, e.g., water in the case of an ammonia-watersolution pair. The refrigerant passes to condenser 40 by means of line21. Condensation of the refrigerant occurs in condenser 40 with theliberation of heat after which the condensed refrigerant is passed fromthe high-pressure condenser 40 to the low-pressure evaporator 50 bymeans of flow control device 60. On heating, the refrigerant evaporatesin the evaporator 50 from which it is passed to the absorber 30 by wayof line 51. Weak solution, e.g., the water remaining from awater-ammonia solution pair after the ammonia has been desorbed byheating in generator 20, is passed from the high-pressure generator 20to the low-pressure absorber by means of flow control device 70. Therefrigerant is combined with (absorbed in) the weak solution with theliberation of heat in absorber 30 to reconstitute the solution pair(strong solution) which is returned to generator 20 by means of pump 24to again repeat the process.

As will be appreciated by those skilled in the art, hundreds ofvariations of the basic absorption cycle that has just been describedare known, e.g., single, half, double, triple effect using a variety ofsolution pairs (working fluids) such as the ammonia-water example notedabove. For example, the heat 32 liberated on the recombination of therefrigerant with the weak solution in the absorber may be provided tothe generator to assist in the heating of the solution pair in thegenerator 20 in what is referred to as a generator-absorber heatexchange (GAX) cycle. However, the present invention is not limited toany particular variation of the basic absorption cycle.

In the present invention, the waste heat source 100 must be capable ofheating the solution pair in the generator 20 of the absorption machine10 to a temperature greater than about 250° F. (121° C.). Preferably thewaste heat source should be capable of heating the solution pair to atemperature greater than about 300° F. (149° C.) and most preferably toa temperature greater than about 350° F. (177° C.).

The waste heat source 100 is not limited to a single source but rathermay include multiple sources. By combining these individual waste heatsources into a single waste heat source 100 and using this single heatsource 100 to heat a single, high-temperature heat exchange fluid loop180, it is possible to service a wide variety of heating needs includingone or more high-temperature (at least greater than 250° F. (121° C.)absorption machines, space heating and process heating requirements. Thehigh-temperature loop comprises a heat exchange unit 111 fortransferring heat from the waste heat source to the high-temperatureheat transfer fluid. Heat exchange unit 22 transfers heat from thehigh-temperature heat transfer fluid to the solution pair in generator20 while exchange unit 146 transfers heat from the high temperature heattransfer fluid to a space or process requiring heat. The various heatexchange units 111, 22, and 146 are interconnected by suitable linesthrough which the high-temperature heat transfer fluid is circulated bymeans of pump 148. High temperature loop 180 can be used to heat manydifferent spaces and processes including multiple high-temperatureabsorption machines. All of the heating needs serviced by thehigh-temperature loop 180 may be generally referred to as thehigh-temperature heating load. One of the key advantages of combiningmultiple waste heat sources to afford a single waste heat source 100that is used to heat a single, high temperature heat exchange fluid loop180 is the elimination and attendant cost savings afforded byeliminating duplicate parts such as pumps that are required ifindividual waste heat sources are used to heat individual heating needs.

Cooler waste heat from exchanger 110 can be used to heat anintermediate-temperature heat-exchange loop 170 that services multipleintermediate heating needs including space and process heating as wellas lower temperature absorption machines. In FIG. 1 such multipleheating needs may be regarded as the intermediate heating load anddesignated generally by the numeral 175. Again as with thehigh-temperature heat exchange loop 180, intermediate-temperatureheat-exchange fluid is circulated from the intermediate-heat exchangeunit 173 to the various loads 175 by means of appropriate lines andsolution pump 176.

Although absorption machines are typically used for cooling purposes, itis to be understood that the present invention also contemplates heatpump type operations in which heat is supplied to the evaporator fromthe outdoors and the absorber and condenser supply heat for space andprocess heating.

When the waste heat source 100 is unavailable for heating or incapableof delivering sufficient heat to meet the solution pair heatingrequirements of the high-temperature absorption machine 10, a secondheating source such as a burner 26 may be used as an alternate heatingsource when the waste heat source 100 is unavailable or to providesupplemental (concurrent) heat when the waste heat source 100 is notfully operational, i.e., insufficient to heat the solution pair ingenerator 10 to an operating temperature. Refrigerant flow device(system) 60 and weak-solution flow device (system) 70, which will bedescribed further below, may be used with any absorption machine 10configuration without regard to solution pair heating requirements.

A heated fluid such as combustion products (exhaust gas), or coolantfluids, i.e., waste heat, from a heat source 100 such as but not limitedto microturbines, diesel or gas engines, fuel cells, and solarcollectors, is passed through a heat exchanger 110 to heat ahigh-temperature fluid in heat transfer unit 111 to a desiredtemperature. Heat exchanger 110 provides a high heat transfercoefficient with little waste-heat stream pressure drop so as not todegrade the performance of heat source 100. The high-temperature fluidfrom heat transfer unit 111 is directed to a heat exchange unit 22 ingenerator 20 of absorption machine 10 via lines 113, 115, 117.

The evaporator 50 of absorption machine 10, which requires the uptake ofheat for the evaporation process, is used to provide cooling to a spaceor process 140 by direct contact with the space or process 140 (notshown) or more typically by means of interconnected heat exchange units141, 143, and a pump 145 to circulate a heat transfer fluid to provideheat from the space or process (load) 140 to evaporator 50, i.e., tocool load 140.

Alternately or simultaneously, the heat high-temperature heat transferfluid from heat transfer unit 111 may be used to provide heat for spaceor process heating, i.e., to heat a second load 190 by means ofthree-way valve 119, line 157 and heat-exchange unit 146. The cooledhigh-temperature heat-transfer fluid from heat-exchange unit 22, orheat-exchange unit 146, or both is pumped back to the high-temperatureheat transfer unit 111 by pump 148 and lines 151, 153, 155. An optionalbypass line 104 may be used to divert waste heat from heat source 100prior to entry into heat exchanger 110. An optional thermal storage tank118 may be used to store hot, high-temperature exchange fluid forsituations such as when the waste heat source only provides heat on anintermittent basis.

An intermediate temperature heating loop 170 may be used to takeadvantage of the intermediate temperature waste heat stream in line 150coming from exchanger 110. The heat in waste heat stream in line 150 ispassed into heat exchanger 172 where the heat is exchanged to a heatexchange fluid in exchange unit 173. The heat exchange fluid passes fromheat exchange unit 173 via line 178 to heat exchange unit 174 where itis used to heat a space or processing load 175. The heating fluid fromexchange unit 174 is returned to heat exchange unit 173 by means of pump176. Processing load 175 could be a generator of an absorptionheat-transfer machine similar to that described above with regard toabsorption unit 10 but operating at a lower temperature, e.g., below250° F. (121° C.) such as is done with a lithium bromide-water solutionpair.

The cooled waste heat fluid stream emerges from heat exchanger 172 vialine 152. As with the high-temperature exchanger 110, a by-pass line 116may be optionally provided for situations in which heating of heatexchanger 172 is not required. As illustrated in FIG. 1, the waste heatfluid stream in lines 104, 116, 152 is illustrated as an open system,that is, the waste heat fluid stream is exhausted to the atmosphere asmight be done with the exhaust stream from a diesel or gas combustionengine. However and as will be appreciated by those skilled in the art,the waste heat fluid stream can be provided as a closed-loop system inwhich a fluid is returned to the waste heat source 100 by means of acirculating pump, as for example, when the waste heat stream is aproduct of lubricating oil or transmission fluid heating.

As shown in FIG. 1, the flow of weak solution from the high to lowpressure side of the absorption heat-transfer machine 10, that is, fromthe generator 20 to the absorber 30 via lines 29 and 28 may becontrolled by fixed or variable flow-control device 70. The simplestmethod uses a fixed restriction (orifice or capillary tube) throughwhich the flow of weak solution is governed by the pressure differencebetween the high and low side pressures. This method is hindered by thefact that the flow rate may be lower than desired during low ambients(reduced high-side pressure) or higher than desired during high ambients(increased high-side pressure). This problem is exacerbated when avariable refrigerant-flow restrictor is utilized, i.e., a thermalexpansion valve as the thermal expansion valve works to maintain an evenlow-side pressure. An improved configuration 70′ for weak solution flowcontrol is shown in FIG. 2 and uses a by-pass loop controlled by asolenoid valve 54. Solenoid valve 54 has a very low pressure drop and isinstalled in parallel with a fixed secondary restrictor 53 by means oflines 81 and 82. A primary fixed restrictor 56 is located downstream ofthe parallel path. That is, and as shown in FIG. 2, the by-pass loopcomprises 1) line 81 connected at one end to line 29 upstream of thefixed secondary restrictor 53 and at its opposite end to solenoid valve54, and 2) line 82 connected at one end to solenoid valve 54 and at itsopposite end to line 29 downstream of fixed secondary restrictor 53 andupstream of primary fixed restrictor 56. The solenoid valve 54 is openedor closed by means of controller 55. Controller 55 may use any number oflogic signals (from process condition sensors 58) to determine the openor closed position of valve 54. Control point sensors 58 include, butare not limited to, a condenser outlet temperature sensor 91 (FIG. 1), ahigh-side (generator 20) pressure sensor 92 in line 29, a low-side(absorber 30) pressure sensor 93 in line 28, a high-low pressuredifferential (pressure sensor 92 signal minus pressure sensor 93signal), a weak-solution temperature sensor 94 in line 29, or agenerator temperature sensor 95 in generator 20 (FIG. 1). Fixed primaryrestrictor 56 is oversized to provide sufficient flow under start-up andlow ambient operation when valve 54 is open. Secondary restrictor 53 issized to provide correct flow under normal operating conditions whenvalve 54 closed.

This method of weak-solution control ensures that adequate weak solutionflow is available during start-ups and low ambient operation (bothduring which the high-side (generator) pressure is low). However, thismethod does not limit the weak solution flow during high ambientconditions (increased high-side (generator) pressure). That is, theincreased pressure encountered during high ambient conditions forces toomuch weak solution through secondary restrictor 53. Primary restrictor56, being oversized for low pressure operation, does little to impedethe increased flow under high-pressure conditions.

FIGS. 3 and 4 illustrate an alternate device 70″ for control of weaksolution flow from generator 20 to absorber 30. A cylindrical flowcontrol valve 57 is used to maintain the flow rate constant over a widerange of inlet and outlet pressures. Valve 57 is installed upstream of afixed primary orifice 58 and is designed to provide a variablerestriction ranging from 5-50% of the total required pressure drop. Theweak solution enters valve 57 housing 89 through the inlet cap 66 andthen enters piston 83 which is moveably mounted in bore 72 formed inhousing 89. Piston 83 has an internal flow path 84 in which a fixed flowcontrol orifice 62 is inserted. As illustrated, the flow path 84composes a longitudinal bore with an as co-extensive with the axis ofthe piston 83 and formed in the piston 83 and valve stem 64 and a radialexit bore connecting at a right angle with the longitudinal bore. Asillustrated, the flow control orifice 62 is formed in plug 85 that isinserted into a bore 88 in piston 83 and sealed by means of seal 86. Theflow control orifice 62 is sized such that when the desired flow rate isachieved, a known pressure drop is obtained. This known pressure dropexerts a known force differential across the piston 83 which in turnexerts a known force on spring 63. Compression of spring 63, whichsurrounds valve stem 64 and contacts a ledge 89 of housing 59 at one endand an end of piston 83, moves the tapered valve stem 64 forward intothe orifice hole 65 formed in outlet cap 67. If the flow increases, thedifferential pressure across the flow control orifice 62 increases andpushes the piston 83 forward and the valve stem 64 farther into theorifice hole 65. This increases the resistance to flow through thestem-impeded orifice hole 65 thereby reducing the flow rate. As aresult, the flow control valve 57 constantly works to maintain a givenflow rate based on the flow control orifice 62, piston 83 diameter,spring 63 constant, and valve stem 64 taper. Seals 61 on the piston 83prevent by-pass flow but allow the piston 83 to move freely withinannular housing 59. This method of weak solution control ensures thatadequate weak solution flow is available at all times without the harshstep-type control of on/off solenoid valve 54. Flow control valve 57controls the flow continuously over the entire range of pressures or canbecome a fixed orifice above a certain high-low pressure differential.

Thermal expansion valves are widely used as a control device for flowcontrol of refrigerant from the high to low pressure side of airconditioning and refrigerating machines based on a vapor-compressioncycle. These valves improve the performance of vapor-compression devicesover a wide range of operating conditions by metering in the exactamount of refrigerant to the evaporator as called for by the load.

Absorption, heat-exchange machines such as device 10 shown in FIG. 1typically do not use a thermal expansion valve as a flow-control device60 in controlling refrigerant flow between the condenser 40 andevaporator 50 because of their high cost. However, with the demand forhigher efficiency HVAC (Heating, Ventilating, and Air Conditioning)equipment and the need to meet the high ambient markets of the AmericanSouthwest, the use of a thermal expansion valve in absorption machines,especially absorption machines using an ammonia-water solution pair isnow justified. However, commercially available thermal expansion valvesfor ammonia are sized (internal restriction) for vapor-compressionsystems which have a lower high-low side differential operatingpressure. Thus a thermal expansion valve designed for 5 RT(refrigeration ton) load in a vapor compression system is capable of 7.5RT in an absorption, heat-exchange machine. Thermal expansion valvesthat are oversized do not function well and result in poor flow control.Smaller thermal expansion valves do not match up well in an absorptionmachine and the resulting higher flow velocities cause premature failureof the valve.

As shown in FIG. 5, a solution to this problem is to use a flow controldevice 60′ that comprises a fixed restrictor 68 and a thermal expansionvalve 69. The fixed restrictor 68 is inserted in front of the thermalexpansion valve 69 with its associated controller 71 so that thedifferential pressure seen by thermal expansion valve 69 is close to itsdesign point. The preliminary fixed orifice 68 must be sized to provideenough restriction to allow the thermal expansion valve to operateproperly under normal operating conditions as well as allowing enoughflow at low ambients (reduced high-side (condenser) pressure).

FIG. 6 illustrates another version of a refrigerant flow control device60″ that allows adaptation of a vapor-compression, thermal expansionvalve to an absorption, heat-transfer machine. In this case, the thermalexpansion valve 69 is installed in parallel with a fixed restrictor 68.The fixed restrictor allows a fixed amount of “base” refrigerant flowunder all operating conditions thereby allowing the thermal expansionvalve 69 to provide a final “trim” flow based on the evaporatoroperating conditions sensed by sensor 71. This arrangement allows asmaller size thermal expansion valve 69 to be used thereby reducingvalve cost and also ensures a minimal amount of refrigerant flow whichin turn ensures a minimal solution flow in the absorption machine 10even when the thermal expansion valve 69 senses that it should beclosed.

It is possible that changes in configurations to other than those showncould be used but that which is shown is preferred and typical. Withoutdeparting from the spirit of this invention, various absorption,heat-transfer cycles and heat exchange devices may be used.

It is therefore understood that although the present invention has beenspecifically disclosed with the preferred embodiment and examples,modifications to the design concerning sizing, shape, andinterconnection of components and heat-transfer among components will beapparent to those skilled in the art and such modifications andvariations are considered to be equivalent to and within the scope ofthe disclosed invention and the appended claims.

1. An absorption, heat-transfer system comprising: a) a first absorptionheat-transfer machine comprising a first generator, an absorber, acondenser, and an evaporator operatively connected together; b) saidgenerator and said absorber having a first flow control device locatedtherebetween and controlling the flow of a weak solution from saidgenerator to said absorber; c) said condenser and said evaporator havinga second flow control device located therebetween and controlling theflow of a refrigerant from said condenser to said evaporator; d) awaste-heat source passing a waste heat stream to a high-temperature heatexchanger for heating: 1) a solution pair in said first generator to atemperature of at least about 250° F. (121° C.) by means of a heatexchange unit in said generator and operationally connected to ahigh-temperature heat-exchange loop comprising a pump and a second heatexchange unit in said heat exchanger for heating a high-temperatureheat-transfer fluid with said waste heat stream from said waste-heatsource; and 2) at least one of the following: a) a heating load by meansof a third heat-exchange unit operationally connected to saidhigh-temperature heat-exchange loop; b) an intermediate-temperatureheat-exchange loop comprising an operationally connected pump, a fourthheat exchange unit in an intermediate temperature heat exchanger, and afifth heat-exchange unit for heating a second load by means of saidwaste heat stream emerging from said high-temperature heat exchanger. 2.The absorption, heat-transfer system according to claim 1 wherein saidsolution pair in said first generator is heated to a temperature of atleast about 300° F. (149° C.) by means of said heat exchange unit insaid generator.
 3. The absorption, heat-transfer system according toclaim 1 wherein said solution pair in said first generator is heated toa temperature of at least about 350° F. (177° C.) by means of said heatexchange unit in said generator.
 4. The absorption, heat-transfer systemaccording to claim 1 wherein said solution pair in said generator iswater and ammonia.
 5. The absorption, heat-transfer system according toclaim 1 further comprising a second heat source for heating saidgenerator of said absorption, heat-transfer machine.
 6. The absorption,heat-transfer system according to claim 1 further comprising a firstline for passing at least a portion of said high-temperature heattransfer fluid to said heat exchange unit in said generator of saidabsorption heat-transfer machine and a second line for of passing atleast a portion of said high-temperature heat-transfer fluid to saidthird heat exchange unit for heating said heating load.
 7. Theabsorption, heat-transfer system according to claim 6 wherein saidhigh-temperature heat transfer fluid is passed to said heat exchangeunit in said first generator and to said third heat exchange unit bymeans of a three-way valve.
 8. The absorption, heat-transfer systemaccording to claim 1 further comprising a thermal storage tank forstoring said high-temperature heat-transfer fluid after heating by saidwaste-heat stream.
 9. The absorption, heat-transfer system according toclaim 1 wherein said high-temperature heat-transfer fluid is heated bysaid waste-heat stream in said high-temperature heat-exchanger by meansof a line connected to said waste heat source, said line having ahigh-temperature heat-exchanger by-pass line.
 10. The absorption,heat-transfer system according to claim 1 wherein saidintermediate-temperature heat-transfer fluid is heated by saidwaste-heat stream in said intermediate-temperature heat-exchanger bymeans of a line connected to said high-temperature heat-exchanger, saidline having an intermediate-temperature heat-exchanger by-pass line. 11.The absorption, heat-transfer system according to claim 1 with saidwaste-heat stream heating an intermediate-temperature heat-transferfluid in said intermediate-temperature heat exchanger; said intermediateheat-transfer fluid heating said second load with said second loadcomprising at least one of the following: i) a space; ii) a processingbad; and iii) a second absorption heat-transfer machine.
 12. Theabsorption, heat-transfer system according to claim 11 with saidintermediate heat-transfer fluid heating said space.
 13. The absorption,heat transfer system according to claim 11 with said intermediateheat-transfer fluid heating said processing load.
 14. The absorption,heat-transfer system according to claim 11 with said intermediateheat-transfer fluid heating said second absorption heat-transfermachine.
 15. The absorption, heat-transfer system according to claim 1with said first flow control device comprising: a) a first restrictorreceiving said weak solution from a first line connected to saidgenerator and passing said weak solution to said absorber with a secondline; b) a second restrictor located in said first line between saidgenerator and said first restrictor; c) a weak solution, by-pass linearound said first restrictor comprising an on-off flow device.
 16. Theabsorption, heat-transfer system according to claim 15 wherein saidon-off flow device is operated by a controller.
 17. The absorption,heat-transfer system according to claim 16 wherein said controller isconnected to an absorption cycle sensor.
 18. The absorption,heat-transfer system according to claim 1 with said first flow controldevice comprising: a) a fixed restrictor receiving said weak solutionfrom a first line connected to said generator and passing said weaksolution to said absorber with a second line; b) a variable restrictorpositioned in said first line between said generator and said firstfixed restrictor.
 19. The absorption, heat-transfer system according toclaim 18 with said variable restrictor comprising: 1) a housing having acylindrical bore formed therein for receiving said weak solution at afirst end and outputting said weak solution at a second end; 2) acylindrical piston with a first end and second end; a) moveably mountedin said cylindrical bore and having a common longitudinal axistherewith; b) having a bore formed therein to pass said weak solutionfrom said first end to said second end; and c) having a valve stem atsaid second end; said valve stem moveably engaging an orifice in saidsecond end of said housing; and 3) a helical spring positioned aroundsaid valve stem and contacting said second end of said piston at one endand a shoulder of said housing at a second end.
 20. The absorption,heat-transfer system according to claim 1 with said second flow controldevice comprising: a) a thermal expansion valve receiving saidrefrigerant from a first line connected to said condenser and passingsaid refrigerant to said evaporator with a second line; and b) a fixedrestrictor located in said first line between said condenser and saidthermal expansion valve to reduce the inlet pressure to said thermalexpansion valve.
 21. The absorption, heat-transfer system according toclaim 1 with said second flow control device comprising: a) a thermalexpansion valve receiving said refrigerant from a first line connectedto said condenser and passing said refrigerant to said evaporator with asecond line; and b) a refrigerant, by-pass line around said thermalexpansion valve comprising a fixed restrictor for passing a fix amountof refrigerant from said condenser to said evaporator.
 22. Aweak-solution flow control device for an first absorption heat-transfermachine comprising a generator, an absorber, a condenser, and anevaporator operatively connected together, said flow control devicecomprising: a) a first restrictor receiving said weak solution from afirst line connected to said generator and passing said weak solution tosaid absorber with a second line; b) a second restrictor located in saidfirst line between said generator and said first restrictor; c) a weaksolution, by-pass line around said second restrictor, said by-pass lineconnected at one end to said first line upstream of said secondrestrictor and at a second end to said first line downstream of saidsecond restrictor and upstream of said first restrictor and comprisingan on-off flow device.
 23. The absorption, heat-transfer systemaccording to claim 22 wherein said on-off flow device is operated by acontroller.
 24. The absorption, heat-transfer system according to claim23 wherein said controller is connected to at least one absorption cyclesensor.
 25. A weak-solution flow control device for an first absorptionheat-transfer machine comprising a generator, an absorber, a condenser,and an evaporator operatively connected together, said flow controldevice comprising: a) a fixed restrictor receiving said weak solutionfrom a first line connected to said generator and passing said weaksolution to said absorber with a second line; b) a variable restrictorpositioned in said first line between said generator and said firstfixed restrictor.
 26. The absorption, heat-transfer system according toclaim 25 with said variable restrictor comprising: 1) a housing having acylindrical bore formed therein for receiving said weak solution at afirst end and outputting said weak solution at a second end; 2) acylindrical piston with a first end and second end; a) moveably mountedin said cylindrical bore and having a common longitudinal axistherewith; b) having a bore formed therein to pass said weak solutionfrom said first end to said second end; and c) having a valve stem atsaid second end; said valve stem moveably engaging an orifice in saidsecond end of said housing; 3) a helical spring positioned around saidvalve stem and contacting said second end of said piston at one end anda shoulder of said housing at a second end.
 27. A refrigerant flowcontrol device for a first absorption heat-transfer machine comprising agenerator, an absorber, a condenser, and an evaporator operativelyconnected together, said flow control device comprising: a) a thermalexpansion valve receiving said refrigerant from a first line connectedto said condenser and passing said refrigerant to said evaporator with asecond line; and b) a fixed restrictor located in said first finebetween said condenser and said thermal expansion valve to reduce theinlet pressure to said thermal expansion valve.
 28. A refrigerant flowcontrol device for a first absorption heat-transfer machine comprising agenerator, an absorber, a condenser, and an evaporator operativelyconnected together, said flow control device comprising: a) a thermalexpansion valve receiving said refrigerant from a first line connectedto said condenser and passing said refrigerant to said evaporator with asecond line; and b) a refrigerant, by-pass line around said thermalexpansion valve comprising a fixed restrictor for passing a fix amountof refrigerant from said condenser to said evaporator.